The conversion of IMP to GMP is catalyzed by the consecutive action of IMP dehydrogenase and GMP synthetase encoded by guaB and guaA, respectively. The former enzyme is the first committed step in GMP synthesis. The latter enzyme catalyzes the replacement of an oxygen atom at the 2-position of XMP with an amino group, utilizing either L-glutamine or ammonia. The specific kinase product of gene gmk converts GMP to GDP. GMP can also be supplied by a salvage pathway as indicated by the pathway link. However, rapidly growing cells may require more GMP than can be supplied by the salvage pathway (reviewed in [Hedstrom09]).

In bacteria, genetic studies have indicated that the majority of de novo purine biosynthetic genes are unlinked, but may act as a single unit of regulation controlled by the PurR repressor protein [Meng90].